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Atlas overhaul...stop me before its too late!

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#1 Brodie

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Posted 27 May 2009 - 10:19 PM

i've had my atlas eq-g for over a year now. i think i'm ready to open it up and give it a tune.
a few questions:
i know i should super-lube (pack) the bearings...but what about the worm gear. same stuff?
i've heard that this mount out of the box yields about 20 arc secs in periodic error...but a good grease job can get it down to single digits. (is that accurate?)
what is the easiest way to verify the before and after peridic error? (i have no webcam...)
Finally, what am i about to get into? should i even attempt it given that i am not an aerospace engineer (though i did tour NASA once)

#2 Skylook123

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Posted 27 May 2009 - 11:57 PM

:lol: If it ain't broke...

#3 John Carruthers

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Posted 28 May 2009 - 02:04 AM

Yes the same lube works all over, there are no fast moving parts. The bearings don't need to be packed, a light smear is enough, in fact if the rollers skid instead of rolling they can develop flats.
Things to consider are controlling end float on the worm (needs thrust washers)and the condition of the worm bearings (new will help, fancy ceramic are available). There is no locknut or similar to stop the end float adjustment drifting, another locking ring or some Loctite/nail varnish will help. Maybe drill/tap for a small grub screw here?
The worm axis needs to be on the gear centre line, this is controlled by nylon ring spacers, they may need to be thicker/thinner, teflon sheet is good.
The casting isn't very thick and will flex as the worm mesh is adjusted, allow for some relaxation and work the worm right round the wheel by hand feeling for tight spots.
Note the difference between the RA and dec motor mounting slots, a magnetic screwdriver is a boon when refitting them.
The second thing to do after removing the conector panel is to disconect the polar axis illuminator led. Otherwise it will twist the wires and break when you unscrew the polar axis.
I clean all parts in turps sub with a toothbrush then pop them into the ultrasonic cleaner for a few seconds - shiny :-)
If you have the parts to hand and hit no snags they can be done in a morning.

#4 Time on my hands

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Posted 28 May 2009 - 03:05 AM

"If it ain't broke... " it will be soon. My Atlas does not appear to be unusual in what I found inside. Metallic dust almost everywhere and metal turnings (As in from a lathe!) were stuck to the grease on the Dec axis shaft behind the electronics. None of these things kept it from performing the light duty it saw during the first two years. However, how long would it have been before a turning broke loose and got into a bearing or the electronics? I did not want to find out.

#5 rmollise

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Posted 28 May 2009 - 07:23 AM

:lol: If it ain't broke...


Ain't that the truth...or as one of my mentors, Senior Chief James L. Turner (Ret) used to preach to me:

"The Only Enemy of Good Enough is More Better."

If the mount is doing its job, leave it alone. Attempts to turn it into a Tak or an AP are destined to fail, and have often resulted in _disaster_.

#6 Brodie

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Posted 28 May 2009 - 08:49 AM

its not just for PE reduction. with the 10" OTA, finder, and DSLR, the mount is at its payload limit (or at least the advertised limit). i am worried about the overstress on the gears, and the wear of the bearings.
but i am also just as scared to screw it up in an overhaul attempt.
perhaps i should shell out $450 and send it to Astro Motion???

#7 Charlie Hein

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Posted 28 May 2009 - 09:02 AM

If you just can't enjoy your hobby without having completely rebuilt your rig then by all means enjoy your tear down and rebuild.

That said, unless you have an observed problem that you want to correct my considerable experience here is that it is best to leave sleeping dogs lie.

Rule of thumb on tearing your mount down - if you can't *exactly quantify* something that you need to fix then leave it be.

About reducing PE - a tear down and rebuild probably won't lower your PE enough to really make the process worth the effort. Autoguiding will correct for a huge amount of PE (way more than you would think), and you will never get the mount to the point where you can do serious astrophotography without autoguiding anyway. If you get good performance while guiding then this removes PE as a need for a rebuild.

If your autoguider is having trouble correcting fast "spikes" in PE and you're stars are not round because of this then perhaps a cleaning and regreasing is in order - but the goal is not to reduce the PE - it is to remove the "spikes". There's a big difference in intent as well as expectation.

If you find that the mount is "stiffening up" considerably when loaded up as opposed to when it is unloaded then maybe a regrease is in order. At this time you may want to replace the bearings with higher grade units, especially if you are continually pushing the load limit of the mount. Make sure that you can't adjust the stiffness out first though.

#8 John Carruthers

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Posted 28 May 2009 - 12:36 PM

:lol: the last one had 2 major chunks of swarf, one bedded into the root of the worm wheel teeth :foreheadslap: and one just floating around in the grease, ugh.
Loads of grit left in the wash tray too and it was only 18 month old, light duties.

#9 Brodie

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Posted 28 May 2009 - 12:45 PM

well, these mixed opinions sure isnt making the decision any easier. i am confident that i could take the thing apart, give it a good cleaning, regrease, and put it back together. i'm not as confident with any mods, such as finding the right nylon spacer, correcting the end floats and such...
will have to give it more thought.
edit: Charlie, i hear what you are saying, but, since im close to its payload limit now, i will certainly be over it once i add a guide scope and guide camera. want to be certain the gears have all the advantage they can get. perhaps i should just downsize the OTA?

#10 astro_baby

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Posted 28 May 2009 - 01:27 PM

I stripped down my HEQ5 ( same as Sirius mount ) and rebuilt it. I didn't go getting micrometers out to measure the nylon spacers. JUst a simple strip, clean, regrease and rebuild.

Its not actually that hard so long as you have some basic tools, are careful and have a lot of patience. Easily the toughest thing on the HEQ5 was getting the gear engagement right on the RA.

So long as your careful theres not much you can badly screw up with it.

I'm not a mech engineer by trade ( I'm a secretary ) but I have taken car engines to bits before and got them back together. Its mostly common sense and patience.

The scare factor for me was there weren't any really good guides around or workshop manuals so I worte my own as I went along.

My HEQ5 wasnt that old - about 12 months - but I found a fair amount of swarf inside, very undergreased bearings and a REALLY huge paint chip inside.

I;d probably never have gotten round to stripping it down but I did a GoTo upgrade and the motors started binding badly afterwards. I decided to completely strip and see if I could make it better.

I cant tell you the PEC values as I dont do imaging and frankly, I'd have no idea how to obtain them. What I can tell you is that after the strip and rebuild and regrease the mount runs smoother, quieter and is more free flowing in its movements. Before the rebuild it always fealt as if there was some treacle inside.

Mine didnt have the famous black goop as a lube - it seemed to be filled with a heavy suty automotive lubricant rather like Castrol grease but it was very badly underlubed especially on the taper bearings.

I cant say for the Atlas how long a strip down takes - the HEQ5 took a whole day with me moving at a slow pace and taking my time. It took another 2 days to get the worm engagement right because its a lot of messing about.

#11 Skylook123

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Posted 28 May 2009 - 02:43 PM

After three-plus years with my Atlas, and just as long on the Yahoo group watching and learning other folks' experiences, the one factor that jumped out at me was the use of solvent to clean the old lubrication and causing the spacers to dissolve. I would think the rest of the process can be accomplished without much diffidulty except that the final mesh adjustments can be a bit tedious. Just don't ruin the spacers unless you have a spare kit.

#12 Charlie Hein

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Posted 28 May 2009 - 03:32 PM

Charlie, i hear what you are saying, but, since im close to its payload limit now, i will certainly be over it once i add a guide scope and guide camera. want to be certain the gears have all the advantage they can get. perhaps i should just downsize the OTA?


Most of the guys in my club that own an Atlas are running refractors in the 80-120mm range as the main imager with a smaller refractor as the guide scope. The mount is a bona-fide killer with this load - excellent tracking and guiding from every single one of them that's outfitted this way.

I think a manageable heavier setup is a C-8 SCT OTA and a refractor in the 66 to 110mm range, but to me this is about as far as I would go. I myself have run the C-9.25 with and without a guide scope (using an SBIG ST series camera) and although the mount will carry the load I much prefer running without the extra weight using the C-9.25. It's a matter of keeping the vast majority of the frames you take - generally speaking the heavier the load, the more frames that will need to be tossed out.

That said you're going to see where folks load it up big time - one guy in our club runs a C-11 Hyperstar with a guidescope - this is not a task for the faint of heart.

Bottom line - if you load the mount up and all of a sudden you cannot balance in DEC because no matter where you set the load the DEC won't turn, you *may* be a candidate for better bearings. If you're loaded all the way up and balancing is easy to attain then look for another reason to do the teardown.

...and remember, if you trust your skills and the job is just calling out to you then by all means go have some fun!

#13 Brodie

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Posted 28 May 2009 - 03:35 PM

how do you know when youve got the "worm engagment/mesh adjustment" right....is it ajust/put back together/track/tear down/adjust....ect?

#14 astro_baby

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Posted 28 May 2009 - 04:53 PM

The worms are adjusted by two things - the worm engagement and the end float. If these are too loose the mount will have excess 'play' if too tight the gears/motors will bind and stall (you get a nasty grinding sound like a blender trying to blend bolts ).

To set the worm engagement ( assuming you arent going the whole hog and fitting shims, bigger or smaller washers etc ) you have to get the worm carrier gear lined up. This is done by adjusting a pair of set screws that control how close to the worm gear the worm is. Its a pain for the RA worm more than the DEC. DOnt ask me why it just is.

Basically you loosen one screw and tighten the other until play goes away and then use either the motors or, with the motors removed run the gears by hand, to drive the mounts axis ( ie if adjueting the RA then move the RA axis) through 360'. If theres any binding you slacken it off until there isn't any and your there. Sounds easy BUT quite often you'll find its adjusted so that the play has gone BUT its just a teensy bit too tight and the motors wont run OR the motors are fine but there's excess play in the mount OR it seems fine but the motors will stall at one single point in the 360' rotation which means the worm carrier may be a little skew. Its made tougher by the fact that when you adjust the set screws you have to slacken slightly the carrier bolts. When these are tightened up sometimes theres a small slippage and you have to adjust again.

The worm float adjustment is similar. You have to adjust them enough so that play goes away but the mounts motors can shift the mount round. Here's the catch - BOTH can cause the same problem so you have to use both the worm carrier adjustemnt and the end float to get to a point where theres no play/minimal play but everything is smooth on motor power.

I do it by adjueting the womrs first just to get them loosely in, just far enough to be about lighgtly habd tight - set the worm engagement and then slowly adjust the float.

Its not hard to do but it does require a lot of patience to slowly work through it and accept that initially the first few times its going to be wrong.

Like collimation its something you can fiddle with eternally.

On my HEQ5 theres always some small play in the mount once its loaded up with my 8" scope. I compared this to a factory fresh unit and there always is a teensy amount of play - if you push the front or back of the scope ot he mount will show a tiny (less than 1 mm play) when pushed.

On the HEQ5 thats probably just a consequence of the length of the scope acting as a very efficient lever.

Anyway thats it really. I toyed with the idea of making up teflon shims and having the worms and worm gear specially machined to get them perfect BUT at the end of the day I only observe and I transport the scope and mount for each viewing session so that level of precsion would be wasted on me.

The HEQ5 though now tracks perfectly, its so quiet you wouldnt even know its there even on a silent night when slewing fast and unlike a lot of HEQ5 owners I find alignment is near perfect every single time with the first alignment star nearly always VERY close to the centre of the FOV. Whether the rebuild helped with that I dont know as prior to the rebuild it never had GoTo but I have seen lots of posts from people who say that even though all the right data has been entered the mount misses its targets on alignment by a large degree.

As much as anything though messing with the mount taught me quite a bit and on the whole it was fun but then I like messing about with stuff and seeing whats inside.

#15 Brodie

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Posted 28 May 2009 - 05:10 PM

thanks guys..very helpful.

#16 rmollise

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Posted 28 May 2009 - 05:24 PM

its not just for PE reduction. with the 10" OTA, finder, and DSLR, the mount is at its payload limit (or at least the advertised limit). i am worried about the overstress on the gears, and the wear of the bearings.
but i am also just as scared to screw it up in an overhaul attempt.
perhaps i should shell out $450 and send it to Astro Motion???


As long as you keep things balanced, there is nothing to worry about. If you have problems THEN tear it to pieces... :lol:

#17 Rudy Nix

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Posted 28 May 2009 - 07:47 PM

I am currently in the process of rebuilding my Atlas. It is completely disassembled at the moment and am waiting on one bearing (32208 J2/Q) that is currently on back order. There are two really great web sites that document tear down and assembly for the Atlas which I am using as guides for my rebuild. Here they are:
http://www.beevo.com/rework.htm
http://www.stonyhill...ry.com/eq-6.htm
If you do decide to tackle the rebuild, they may help considerably.
Rudy

#18 Rusty

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Posted 28 May 2009 - 10:50 PM

"If it ain't broke..." fix it until it is. :grin:

I'm probably one of the more-qualified CNers to discuss lubricants...

First, about destoying spacers with solvent...this is why I preach (ad nauseum) to use only mineral spirits (but there are other reasons why other solvents are unwise).

Anyway, I've cleaned and relubed many mounts, yet I've not messed with my Sirius EQ-G nor the Tak NJP (the latter, I regreased some things when I replaced the Dec motor bracket).

The reason is: They work just fine.

#19 mtb.daily

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Posted 28 May 2009 - 10:50 PM

Rudy,

You're waiting on the bearings.
Those, I have. I am waiting on the grease....

:(

#20 dvb

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Posted 28 May 2009 - 11:08 PM

I'm running a 45 lb. OTA on EQ6, and it is handling it beautifully - No odd noises or funny movements -- but I'm still tempted to have a look!

Astro Baby, your experience is encouraging - and made me miss my HEQ5, which was a very nice, accurate, quiet mount.

#21 Rudy Nix

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Posted 29 May 2009 - 09:30 AM

I have found that there are a lot of hardware items used in astronomy and astrophotography equipment, when purchased from someplace other than a retailer dedicated to astrnomy and astrophotographic equipment, to be almost half the price for an identical item. On one site that sold this bearing, the listed price was $47.00 just for the one bearing. Unfortunatly, the place I ordered the SKF 32208 J2/Q bearing from has them on backorder. I'm willing to wait until they are in stock, especially since they're price is only $27.00.

#22 mtb.daily

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Posted 29 May 2009 - 11:49 AM


The patient process.... Hmmm....... wait.... wait..... wait.....Nope, not for me.

I'll spend the $$$$ and call to be sure they are in stock..... But, thats just me.

#23 groz

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Posted 29 May 2009 - 01:11 PM

"The Only Enemy of Good Enough is More Better."


Truer words were never spoken.

We have an eq6-pro, and an heq5-pro. My eq6 has for the last 6 months carried the C8 in a side by side bar, with the ST80 beside it for guiding. Our heq5 carries a williams 80, and we've got the Kwiq guide system on it (qhy5 in a 9x50 finder). That kwiq works fabulously with this combination, so much so, I decided to try it with the c8.

This last weekend, I removed the side by side setup, and put the kwiq onto the c8. With the focal reducer in the c8, shooting with a canon 350, I got pinpoint perfect stars with this combination too.

Would a tear down/rebuld help either of our kits? I dont think so, they already perform admirably for photography. Would it hurt them ? Maybe, maybe not. I'm not the most mechanically inclined, so, in my case, it's far more likely to hurt rather than help. It aint broke, so, there's nothing to fix, and lots to break.

But, this whole conversation reminds me of a stop at the swap and shop tables at the Table Mountain Star party a couple summers ago. I didn't have the EQ6 yet, and was in the market for a beefier eq mount. One fella had an atlas for sale, but, on close inspection, turned out to be his 'atlas project', complete with 'box of parts left over' after a teardown / put together attempt. That didn't leave me with a warm fuzzy, and I left it sitting on the swap table.

Point of the comments, if you are at all unsure of 'fixing' your mount that is apparently 'not broken', ask yourself how much of a disaster would it be to end up with 'box of parts leftover', and trying to pawn it off at a swap table ? If that would be a dire hardship for you, I'd seriously consider the idea of leaving well enough alone.

#24 John Carruthers

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Posted 30 May 2009 - 02:29 AM

how do you know when youve got the "worm engagment/mesh adjustment" right....is it ajust/put back together/track/tear down/adjust....ect?


2 ways; by feel using years of experience and unerring skill, or hook up a meter and watch the current draw, when it spikes back off a hair.
Once set let it rest for a few minutes then try a full rotation by hand, amazing how much they relax and how much spring there is in the castings.
It's worth persevering to get it as perfect as you can. That way you may never need to do it again. Get that worm fixed lonways, then centred over the wheel, then the mesh depth right. I've seen one that although only a few thou off centre had worn its own 'hog' into the wheel :-(

I would avoid over greasing tapered roller bearings, they're not car wheel bearings and don't need packing as you would for auto aplications, they only go round once a day. The ends need most lube, the sides need to roll along the race not slide. A little pre-load can be good but only a little.

#25 Brodie

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Posted 30 May 2009 - 10:48 PM

i decided to wait atleast until i have a chance to see how it performs with a guide scope. i do think i want to lighten the load with a smaller OTA to help with sturdiness and allow for more accessories....(dang aperture fever).






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